Structure And Function Of The Kidney

Question 1

Where is the kidney located? What is its gross anatomy?

Answer 1

Retroperitoneal space. Between 11th thoracic and 3 lumbar vertebra. Either side of vertebral column. Right situated slightly lower than left.

12cm long. 150g in males and 135g in females.

Question 2

Describe the renal blood supply

Answer 2

Makes up 25% of cardiac output. 90% of which supplies renal cortex

Question 3

What path is taken after the kidney?

Answer 3

Down the ureter to the bladder and then excreted out of the body through the urethra

Question 4

What are the three major functions of the kidneys?

Answer 4

Maintain water and kidney homeostasis
Remove water soluble waste products and toxins
Produce and respond to chemical messengers

Question 5

What is the functional unit of the kidney?

Answer 5

The nephron- 0.4-1.2 million per kidney

Each nephron has 5 functional units; glomerulus, proximal tubule, loop of henle, distal tubule and collecting duct

Question 6

What is the glomerulus?

Answer 6

Specialised capillary network enclosed within Bowman’s capsule.
Form an ultra-filtrate of plasma; maintain important constituents, like blood cells, of the blood but remove excess fluid, waste products and regulate H+, Na+ and K+

Question 7

What makes up the glomerular filtration barrier?

Answer 7

Endothelium, basement membrane and podocytes

Question 8

What does not enter lumen of glomerulus?

Answer 8

Blood cells, proteins >50kDa and more negatively charged proteins

Question 9

What is the proximal consulted tubule?

Answer 9

Bulk reabsorption of electrolytes from the glomeular filtrate back into circulation
Active: Na+
Passive: Glucose, amino acids, HCO3-, K+, HPO4
Secretion: H+, organic anions and cations

Question 10

What is the loop of henle?

Answer 10

Consists of descending and ascending limbs; down from cortex into the medulla and back up again
Responsible for creating hyperosmolar medulla - necessary for production of concentrated urine.
Utilised counter current multiplication system; creates dilute urine after H2O load or concentrated urine after H2O restriction

Question 11

Outline counter current multiplication

Answer 11

1) descending limb highly per able to water. IncreAsed osmolality of interstitium causes water to be absorbed, concentrating the tubular fluid.
2) ascending limb is impermeable to water, but resorbs solute from the tubular fluid. Making fluid more dilute.
3) fluid reaching the collecting duct is hyposmotic
4) vasa recto capillary removes water reabsorbed from descending limb to maintain high medullary osmolality
5) result is hypertonic medullary fluid compared to filtrate that enters the distal convoluted tube

Question 12

What is the function of the distal convoluted tubule?

Answer 12

Carry out fine-tuning of electrolyte resorption and secretion
Specifically Na, K and H
Under hormonal control

Question 13

What is the function of the collecting duct?

Answer 13

Reabsorption of water
Naturally impermeable to water
ADH stimulation causes aquaporins to move to membrane and allow water to pass in
Passive diffusion due to action of counter-current multiplication system

Question 14

What does to kidney need in order to function?

Answer 14

Adequate perfusion
Positive partial pressure at the glomerulus
Viable, semi-permeable glomerulus membrane
Intact function in tubular endothelium
Clear passage for filtrate to travel
Appropriate hormonal activity/ability to respond

Question 15

How can renal function be assessed?

Answer 15

Assessment of glomerular filtration - ability to remove waste
Assessment of glomerular filtration - ability to select what enters the tubules
Assessment of tubular cell function - ability to secrete or reabsorb and ability to respond to stimulation

Question 16

What 5 characteristics would an ideal marker of glomerular filtration have?

Answer 16

1) Endogenously produced
2) appears in plasma at constant rate
3) freely filtered by glomerulus
4) not reabsorbed or secreted by renal tubules
5) not eliminated extra-renally

Question 17

What two markers of glomerular filtration are used?

Answer 17

Urea: derived from amino acids in liver. Removed by kidneys.
Creatinine : produced at constant rate from muscle creatine breakdown. Serum/plasma blood test. Not obvious until kidney function below half.

Question 18

What is glomerular filtration rate (GFR)?

Answer 18

Expression of quantity of filtrate firmed each minute in the nephrons of both kidneys, calculated by measuring the clearance of a specific substance

Question 19

How is creatinine clearance calculated?

Answer 19

Requires both serum and 24hour urine sample.
Can pick up small changes in renal function
(Urine creatinine * urine volume)/ (serum creatinine *time)

Question 20

What is estimated GFR?

Answer 20

More sensitive then creatinine clearence and only requires serum sample
But cannot be used for ill patients, elderly patients, pregnant patients, obese or malnourished
Uses formulas that try to correct for variables, but is still affected by muscle mass; Cockcroft, MDRD, CKD-EPI and Schwartz

Question 21

How can very accurate GFR be calculated?

Answer 21

Exogenous markers

Disappearance of test substance that is completely filtered by glomeruli; insulin and Cr-EDTA

Question 22

What is proteinuria?

Answer 22

Proteins and blood cells in urine due to damage to glomerulus
>3g/24hr
3 types;
Glomerular: damage to glomerulus
Tubular: impaired resorption of small proteins by proximal tubule
Overflow: protein production exceeds reabsorption capacity of the kidney

Question 23

How can proteinuria be tested?

Answer 23

Urine dipsticks
Protein:creatinine ratio
Albumin:creatinine ratio - albumin first protein let through damaged glomerulus
24hr total protein

Question 24

What are the 4 tubular functions?

Answer 24

Ability to excrete an acid load
Ability to concentrate urine
Ability to respond to hormones
Ability to reabsorb solutes, electrolytes and proteins